I agree, just ask the person in charge. I have gotten into several events by just saying who I was and what I do, give the person a card, even if you go to Office Max and have 500 of them printed out for 25 bucks, a business card shows them you are serious about taking photos of their event.
When the event is over send them some proofs and let them know you have images for sale if they are interested. That just might get you "invited" back next year for the same event, or if the event coordinator gets you on file you might get invited to all the events at that particular location.
Good luck.